Other than custom wiring your own switch, you could get a KVM switch with audio. The other choice would be to get an A/B switch for RCA connections, get three mini-stereo (3.5"") to RCA cables and you're set. As for the cables you can pick them up cheap here http://www.monoprice.com. As for the switch, Radio Shack has one for $15 to $20 You can google it and maybe find a better deal

It seems like overkill though for the same price you can pick up a second pair of some decent speakers.